For inspecting solids which may exist in a liquid such as medicine, food and drink, cosmetic, chemicals, reagent or the like, filled in sealed, transparent containers, for example, ampoules, vials, bottles or the like, and to select the containers, there are known various methods for inspection the liquid utilizing the photoelectric element rather than relying simply on the a naked eye inspection.
Among these known methods for inspecting a liquid, the present invention attempts to improve the liquid testing method for determining the intensity of a penetrated light wherein light is projected, for example, through an ampoule) by measuring the degree of the screening of said light due to extraneous substances existing within a liquid by a photoelectric element. In such a case the light is screened by extraneous substances and the light received by the photoelectric element is decreased relative to the amount that is present when an extraneous substance is absent. Therefore, whether the amount of extraneous substances in a liquid is large or small, can be determined according to the decrease of light received by the photoelectric element.